The Ku protein was initially discovered as an autoantigen recognized by sera from patients with polymyositis-scleroderma overlap syndrome. It consists of 70 kDa and 80 kDa subunits and it binds ends of double stranded DNA. The present proposal seeks the biological function of the Ku protein through an effort to identify other proteins with which it interacts. Our preliminary studies indicate that one example is the enzyme DNA-dependent protein kinase (DNA-PK). this enzyme phosphorylates several transcription factors including the carboxyl terminal domain of the large subunit of RNA polymerase II. these studies will seek to demonstrate that Ku and DNA-PK assemble into a macromolecular structure on DNA and they will determine if other proteins participate in this complex. Ongoing efforts to define the forms of DNA which are bound by the Ku heterodimer will be continued. finally, studies will be carried out to determine if there is a coordinated expression of autoantibodies to the various components of the Ku protein-DNA-PK complex in patients with systemic lupus, scleroderma, and polymyositis. These studies will test the hypothesis that Ku protein forms a complex with the 350 kDa catalytic polypeptide of DNA-PK and directs the latter to appropriate sites on DNA where phosphorylation of specific transcription factors is required. It will also test the hypothesis that in the connective tissue diseases selected macromolecular structures are targeted for autoimmune responses with the result that families of autoantibodies are directed against different components of the targeted structure. These studies will lay the foundation for studies which can address how selected "self" structures come into contact with the immune system, either through extrusion from cells or from disruption of assembly, transport, or turnover with the outcome that peptide fragments are inserted into MHC molecules and expressed on cell surfaces for presentation to the immune system.